The invention relates to a method for stacking containers that have been shaped and punched from a sheet of thermoplastic plastic in a shaping tool, and guided to stack magazines, as defined in the preamble to the main claim. The invention further relates to an apparatus for executing the method.
It is known to stack containers that have been shaped and punched from a sheet of thermoplastic plastic in stack magazines, and to remove the stacks from the stack magazines when a specific length or specific piece number is attained, then supply them to successive devices. In these successive devices, either processing takes place, such as bordering of the container edge, or the rods are packaged in foil and transferred to cartons. It is also known to shape the containers in a plurality of rows, with several containers per row, and to guide the stacks consecutively with a transfer device, so they pass through a single bordering station, for example. Stack magazines for receiving the total batch of containers shaped per cycle in the shaping tool are disposed in front of the shaping tool, which is pivoted into the transfer position.
Transporting stacks of specific lengths out of the stack magazines stipulates a certain amount of time. During this time, the shaping tool must continue producing, and the containers must be able to be stacked. German utility model application DE 298 02 318 U 1 proposes to arrange a stationary stack magazine in the stacking station, and above it, a movable stack magazine, with the movable stack magazine being displaceable in both the stacking direction and the direction transverse thereto. The containers are first transferred into the stationary stack magazine, then enter the movable stack magazine after a specified stack height has been attained.
German Patent DE-PS 26 48 563 C 2 likewise discloses transferring the containers into a stationary, lower stack magazine initially, then into a stack magazine that is adjustable in height and lifts a stack once it reaches a specific length or a specific number of containers. A lateral sliding element transfers these stacks to a horizontal receiving sheet.
Handling stacks in this manner does not provide consecutive guidance of the stacks. They would have to be taken up again, a process that would be susceptible to disturbances. A disadvantage of the two cited publications is that, during the time in which the stacks are transferred from the stack magazines, the number of stacked containers depends on the cycle number of the shaping tool. The transfer time of the stacks is constant because of the established paths and speeds of the drives. This means, however, that a varying number of containers is shaped and stacked during this transfer time. This is significant, and is associated with control problems, if stacks are to be formed from a specific number of containers. A further drawback of the two stacking methods is that the containers must be pressed over two stacking edges, which always poses a risk of deformation. As the movable stack magazine returns, it must be pushed across the standing stacks, which can also cause deformation, because each container edge of the standing containers must be guided by these retaining elements. This method of gripping containers is highly susceptible to disturbances, which may necessitate shutting down the shaping machine, cleaning the stack magazines or organizing the containers located in the stack magazines.
It is the object of the invention to execute the method in order to create stacks of a predetermined number of containers, regardless of the cycle number of the shaping tool, and independently of the time required for transferring the stacks to successive devices, even if the apparatus is shut down. The method is intended to be insusceptible to disturbances, and able to be executed even with high cycle numbers of the shaping tool. Furthermore, the method should permit the transfer of container stacks in rows to a successive device, and a fast changeover of the apparatus for a different batch of containers.
The above object generally is achieved according to a first aspect of the invention by a method for stacking containers that have been shaped and punched from a sheet of thermoplastic plastic in a shaping tool, and guided to stack magazines, and for transferring the stacks to a successive device, wherein the containers are transferred into a first stack magazine at a stacking station; after a predetermined number of containers per stack has been attained in the first stack magazine, the first stack magazine is displaced into a stack-removal station, and a second stack magazine is transferred out of the stack-removal station into the stacking station, between two cycles of the shaping tool; and while the containers are being stacked in the second stack magazine at the stacking station, the first stack magazine is emptied, and the removed stacks are guided to a successive device.
The above object generally is achieved according to a second aspect of the invention by an apparatus for stacking containers that have been ejected from a shaping tool after being shaped and punched out with, for executing the method according to the invention wherein two stack magazines, which can be displaced between a stacking station and a stack-removal station are provided.